We have been able to form crystalline complexes of a large number of drug-nucleic acid interactions and to analyze these by X-ray crystallography. This information has led to unifying stereochemical concepts in understanding a large number of drug-DNA interactions, and has given rise to broader implications in understanding protein-DNA interactions. The key stereochemical concept about DNA we have obtained from these studies is the "kink", a stereochemical rearrangement in DNA that allows DNA to bend. This kink may be used in the organization of DNA in chromatin, and may still have wider utilization in other protein-DNA interactions. We have speculated that the RNA polymerase enzyme induces a kinked B DNA structure preliminary to the process of DNA denaturation. We are continuing our drug-nucleic acid cocrystallization studies in an effort to investigate our models of drug-DNA interactions and the "kink". BIBLIOGRAPHIC REFERENCES: "Organization of DNA in chromatin", Henry M. Sobell, Chun-che Tsai, Steven G. Gilbert, Shri C. Jain and T.D. Sakore, Proc. Nat. Acad. Sci. USA 73, No. 9, 3068-3072, (1976). "Mutagen-nucleic acid intercalative binding: Structure of a 9-aminoacridine-5-iodocytidylyl(3'-5')guanosine crystalline complex", T.D. Sakore, Shri C. Jain, Chun-che Tsai and Henry M. Sobell, Proc. Nat. Acad. Sci. USA, 74, No. 1, 188-192 (1977).